Variable sensing using frequency domain

Abstract

Embodiments of a method and apparatus for variable sensing using the frequency domain are taught herein. An exposure of a system to a physical variable is determined by periodically sensing the physical variable to produce a plurality of digital samples. The plurality of digital samples is converted to respective frequency domain representations. The exposure is calculated using the frequency domain representations.

What is claimed is: 
     
       1. An apparatus for monitoring a system responsive to application of a stimulus, the apparatus comprising:
 a memory for storing data; 
 an input channel for sensory input; 
 a processor connected to the memory and the input channel, the processor programmed to:
 receive the sensory input from the input channel as a sequential stream of data samples in a time domain wherein the sensory input is responsive to application of the stimulus to the system; 
 convert the sequential stream of data samples from the time domain to a frequency domain using a Fourier transform to obtain a plurality of complex Fourier coefficients; 
 apply a respective weighting factor to a magnitude of each complex Fourier coefficient to generate weighted magnitudes, each weighting factor based on a relative impact that a particular frequency associated with the magnitude has on the system; and 
 calculate an exposure value for the system responsive to application of the stimulus using the weighted magnitudes; 
 
 an output channel connected to the processor for transmitting an output of the processor external of the apparatus. 
 
     
     
       2. The apparatus of  claim 1 , further comprising:
 a sensing element connected to the input channel. 
 
     
     
       3. The apparatus of  claim 1  wherein the input channel includes amplification and anti-aliasing filters. 
     
     
       4. The apparatus of  claim 1 , further comprising:
 a plurality of input channels for a respective sensory input related to the stimulus, wherein the stimulus is physical stimulus applied from external of the system and the input channel is one of the plurality of input channels. 
 
     
     
       5. The apparatus of  claim 4  wherein the processor is programmed to:
 use the calculated exposure value to trigger receipt of sensory input by a second one of the plurality of input channels. 
 
     
     
       6. The apparatus of  claim 4  wherein the calculated exposure value is a weighted value of outputs of each of the plurality of input channels. 
     
     
       7. The apparatus of  claim 1  wherein the stimulus is applied from external of the system and is other than an audio stimulus. 
     
     
       8. The apparatus of  claim 1  wherein the processor is programmed to convert the sequential stream of data samples from the time domain to the frequency domain using the Fourier transform by:
 assigning at least three arrays to the input channel for receiving the sequential stream of data samples, each of the arrays having a same size; 
 sequentially filling a first array of the at least three arrays with a first number of data samples corresponding to the size; 
 sequentially filling a second array of the at least three arrays with a second number of data samples corresponding to the size, the second number of data samples including some of the first number of data samples at an end of the first number of data samples; 
 performing the Fourier transform on the first array while sequentially filling the second array; 
 sequentially filling a third array of the at least three arrays with a third number of data samples corresponding to the size, the third number of data samples including some of the second number of data samples at an end of the second number of data samples; 
 performing the Fourier transform on the second array while sequentially filling the third array; and 
 performing the Fourier transform on the array window after sequentially filling the third array. 
 
     
     
       9. The apparatus of  claim 8  wherein the processor is programmed to convert the sequential stream of data samples from the time domain to the frequency domain using the Fourier transform by:
 applying a window function scalar to each of the first number of data samples, the second number of data samples and the third number of data samples based on a position of each within the first array, the second array or the third array. 
 
     
     
       10. The apparatus of  claim 1 , further comprising:
 an analog-to-digital converter coupled between the input channel and the processor to digitize the sensory input to form the sequential stream of data samples. 
 
     
     
       11. The apparatus of  claim 1 , further comprising:
 a digital-to-analog converter coupled to the output channel to convert the calculated exposure value to an analog output before transmitting the calculated exposure value external of the apparatus. 
 
     
     
       12. The apparatus of  claim 1  wherein the sensory input responsive to the stimulus is one of acceleration, voltage or temperature. 
     
     
       13. The apparatus of  claim 1  wherein the processor is configured to apply the respective weighting factor to a magnitude by:
 calculating a calibrated power magnitude for each of plurality of frequencies associated with each of the plurality of complex Fourier coefficients by multiplying a calibration scaler for a respective frequency with a square of a magnitude of a complex Fourier coefficient for the respective frequency; and 
 applying the respective weighting factor to each calibrated power magnitude to calculate the weighted magnitudes. 
 
     
     
       14. The apparatus of  claim 13  wherein the processor is configured to calculate the exposure value by:
 summing the weighted magnitudes to obtain a weighted power density spectrum. 
 
     
     
       15. The apparatus of  claim 14  wherein the processor is configured to:
 correlate values of the weighted power density spectrum to a user-defined pattern via a correlation function. 
 
     
     
       16. The apparatus of  claim 13  wherein the processor is configured to calculate the exposure value by:
 comparing the weighted magnitude at a first frequency to a threshold value; 
 generating an exposure value of one when the weighted magnitude at the first frequency is greater than or equal to the threshold value; 
 generating an exposure value of zero or a value of the weighted magnitude at the first frequency divided by the threshold value when the weighted magnitude at the first frequency is below the threshold value. 
 
     
     
       17. The apparatus of  claim 13  wherein the processor is configured to calculate the exposure value by:
 comparing the weighted magnitude at a first frequency to an upper threshold value and a lower threshold value; 
 generating an exposure value of one when the weighted magnitude at the first frequency is greater than the upper threshold value or lower than the lower threshold value; 
 generating an exposure value of zero when the weighted magnitude at the first frequency greater than or equal to the lower threshold value and less than or equal to the upper threshold value. 
 
     
     
       18. A method of monitoring a system responsive to application of a stimulus, the method comprising:
 receiving the sensory input from an input channel connected to a processor as a sequential stream of data samples in a time domain wherein the sensory input is responsive to application of the stimulus to the system; 
 using the processor to convert the sequential stream of data samples from the time domain to a frequency domain using a Fourier transform to obtain a plurality of complex Fourier coefficients; 
 applying a respective weighting factor to a magnitude of each complex Fourier coefficient to generate weighted magnitudes, each weighting factor based on a relative impact that a particular frequency associated with the magnitude has on the system; and 
 calculating, using the processor, an exposure value for the system responsive to application of the stimulus using the weighted magnitudes. 
 
     
     
       19. The method of  claim 18  wherein calculating the exposure value comprises:
 calculating a first exposure value for the system responsive to a first frequency using a first weighted magnitude of a complex Fourier coefficient at the first frequency; 
 calculating a second exposure value for the system responsive to the first frequency using a second weighted magnitude of the complex Fourier coefficient at the first frequency; and 
 calculating a recent exposure value for the system responsive to the first frequency by adding the first exposure value and the second exposure value. 
 
     
     
       20. The method of  claim 18 , further comprising:
 selectively storing the calculated exposure value in a memory connected to the processor based on the calculated exposure value.